1. Field of the Invention
The present invention relates to musical tone generating apparatuses employed in electronic musical instrument for generating musical tones.
2. Background Art
Conventional electronic musical instruments are known in which musical tones are generated based on a plurality of waveform data stored in an waveform memory. The waveform data are digital data which are obtained by sampling a musical tone waveform by a predetermined sampling frequency. When generating a musical tone, tone generating operation is carried out in synchronization with change of sampling periods at which sample data of generated musical tones are to be outputted. In the tone generating operation, an address data, which increases over time at a rate corresponding to the tone pitch of the musical tone, is generated. A plurality of waveform data are read out from the waveform memory based on the integer portion of the address data and an waveform data corresponding to the address data is interpolated based on the waveform data thus read out and the fractional portion of the address data.
In the field of electronic musical instruments, the users require electronic musical instruments which can generate musical tones having high quality and can simultaneously generate many musical tones.
In order to obtain musical tones having high quality, high order interpolation method may be used for electronic musical instruments. In this case, many waveform data are read out from the waveform memory to be used for the interpolation. Therefore, long access time is necessary to supply the waveform data to the tone generating section of the electronic musical instrument.
In order to simultaneously generate many musical tones, time division control is used as control method of electronic musical instruments.
In this type of electronic musical instrument, waveform data corresponding to a plurality of musical tones are generated at sampling periods having a predetermined duration. Each sampling period is divided into a plurality of time division channels. Tone generating operations for generating the musical tones are sequentially carried out by using the time division channels.
In order to increase the number of musical tones to be simultaneously generated, the sampling period should be divided into many time division channels.
However, if the number of the time division channels are increased, the duration of each one of the time division channels become shorter. Therefore, it is difficult to obtain musical tones having high quality. Because, few waveform data can be read out from the waveform memory and the operation to obtain high quality musical tones, for example, high order interpolation, cannot be carried out.
Some users desire electronic musical instruments having an ability to simultaneously generate many musical tones having ordinary quality.
But, the other users require electronic musical instruments which can generate musical tones having high quality.
There are many requirements with respect to the function of electronic musical instruments.
In order to satisfy the requirements of all users, the maker should produce many types of electronic instruments which are required by the users.
However, it is difficult to satisfy such requirements because very high cost is required to produce many types of electronic musical instruments.